The present invention relates to illuminative apparatus, more particularly to illuminative apparatus of the type wherein starting means is employed for preheating the electrodes of a fluorescent lamp.
Conventional fluorescent lamps are electric discharge lamps in which gas ionizes and produces radiation which activates fluorescent material inside glass tubing. Generally, a fluorescent lamp includes a phosphor-coated tubular bulb which has electrodes sealed into each end and which contains mercury vapor at low pressure along with an inert starting gas (e.g., argon or an argon-neon mixture). The tubular bulb has been practiced in a variety of shapes but is usually of straight, U-shaped or circular configuration. When the proper voltage is applied across the ends of the tubular bulb, an arc is produced by current flowing between the electrodes through the fill gas. The ultraviolet energy from the arc excites the phosphor coating to emit light; i.e., the phosphor coating transforms some of the ultraviolet energy generated by the electric discharge into light.
The visual sensation of abrupt change in the illumination intensity or brightness of a stationary object is known as "flicker." "Cyclic flicker" is normally inherent in lighting systems which are supplied with alternating current (ac). The light which is emitted from a fluorescent lamp or an incandescent lamp which is operated on ac circuitry typically executes these cyclic pulsations. The cyclic flicker associated with fluorescent lamps is generally of considerably greater magnitude than the cyclic flicker associated with incandescent lamps. Nevertherless, in normal usage the cyclic flicker associated with either fluorescent lamps or incandescent lamps is generally not readily visible.
Sometimes a fluorescent lamp commences another kind of flicker when it is in a malfunctioning mode, often toward the end of its useful life. This abnormal flicker is referred to herein as "blinking." Blinking, as distinguished from cyclic flicker, is an aberrant phenomenon and frequently is visibly appreciable. Blinking generally results from voltage fluctuations caused by sudden variations in load, and may be regular or irregular. Sometimes blinking regularly recurs in accordance with a regular succession of voltage dips; such regular recurrence may be rapid. Other times blinking recurs irregularly, in terms of frequency of occurrence and/or duration, in accordance with corresponding irregularity of voltage dips.
Blinking not only is energy-inefficient but also forewarns a possible fire hazard. The inordinate heating, by excessive voltage, of a component of the fluorescent lamp circuitry represents a potentially combustible situation. Moreover, fluorescent lighting has been known to interfere with proper functioning of digital computers, televisions, radios, remote control devices and other forms of electronic apparatus. See, e.g., "Interfering Fluorescents," Popular Science, September 1994, page 50. Electronic equipment has been observed to be especially vulnerable to such interference when the infrared signal emissions from a fluorescent lamp are erratic due to voltage fluctuations associated with blinking of the lamp. Although circuit-breaking capability has been known to be utilized in connection with fluorescent illumination, in conventional practice the actual breaking of the circuit may not be effectuated in timely enough fashion to have avoided significant deleterious effects of malfunctioning associated with blinking.
A blinking light may be inconspicuously located. Even when a blinking light is noticeable, its impact upon an observer can vary. The degrees of perceptibility and objectionability of observed fluorescent blinking correspond to the change in light output in terms of frequency and magnitude, and are affected by several factors such as lamp size, lamp type, illumination level, voltage dip rate of change, voltage dip duration, surrounding brightness and the observer's physiology/psychology. See, e.g., Davidson, G. E., "Flicker in Lighting Systems (Effect of Sudden Voltage Dips Studied)," Ontario Hydro Research News, October 1952, vol. 4, no. 4, pages 9-11.
Human nature is such that one may need to be externally motivated in order to act in a responsible manner with regard to some occurrence or state of affairs in one's life. When a blinking fluorescent bulb is noticed, it may not, in and of itself, be annoying or bothersome enough to motivate someone to replace the bulb or otherwise correct the underlying problem, or even to simply terminate operation of the bulb. A person may be particularly neglectful when there remain properly functioning fluorescent bulbs which that person views as sufficiently compensating for the light deficiency or as sufficiently alleviating the disturbance.